The technique of nuclear magnetic resonance has been used to examine the properties of fluorinated amines inside platelets. In pig platelets, fluorinated quinacrine added to the vesicles assumes motional properties similar to those of the other vesicular contents. In human platelets, 5-fluorodopamine sulfate appears to be retained in the cytoplasm. Proton nuclear magnetic resonance studies of amino acids and glucose metabolism in cells and living tissues appear to be feasible. Alcohol alters the relaxation behavior of water protons in red blood cells and plasma.